Accelerometers, pressure sensors, and other devices sometimes use electrostatic comb drives to provide feedback-force in a closed-loop configuration. The drive consists of one or more sections of lateral comb teeth pairs. Each pair has a tooth attached to a moveable proof mass (accelerometer) or diaphragm (pressure sensor) and another tooth attached to a fixed frame. Since an electrostatic force between the teeth pairs is always attractive, the variety of ways to configure the comb teeth is limited. In an accelerometer, a common way to structure the drive of the device is to have two drive sections, one to provide the feedback force for positive input and one for negative input. One of the two drive sides would be on each side of a centerline, see FIG. 1, which represents current-art. A common problem that occurs in current-art devices is that the gaps between the fixed and moveable teeth don't remain constant, over time and/or through environmental inputs, and thus the electrostatic force, which is inversely proportional to the square of the gap, also will vary. In closed-loop operation, a change in the gap results in a change in the applied differential voltage across the gap necessary to balance the inertial force on the proof mass. This voltage is used as the indicator of the sensed acceleration, and thus, an apparent change in acceleration occurs. This is seen as an error in the instrument's scale factor. For example, if the gap increases by 1%, then the instrument's scale factor will increase by about 2% (a 2% error). Gap variation may be caused by environments such as temperature variation, shock, or long-term storage. For example, if the proof mass and all the teeth are made of Silicon but the fixed teeth are attached to a frame made of another material, e.g., glass, then a temperature change will cause the fixed and moveable teeth to expand at different rates and move relative to one another. Generally, the geometric center of both the moveable teeth on the proof mass and the fixed teeth attached to the glass will remain coincident, but each will expand radially at different rates. The further from the geometric center that a tooth pair gap is located, the greater the rate of change of that gap with temperature, and thus the greater the effect on the instrument scale factor.
Therefore, there exists a need for a comb drive configuration, which acts to remove this source of error.